ACCESS TO RANDOM RESOURCE UNITS BY A PLURALITY OF BSSs

ABSTRACT

A physical AP manages a plurality of BSSs through VAPs. The AP sends a trigger frame to reserve a TXOP including resource units the nodes access to transmit data during the reserved TXOP. To improve channel utilization, the trigger frame identifies a plurality of groups, nodes of which are allowed to access the resources units to transmit data during the reserved TXOP. Thus, the AP receives, during the reserved TXOP, data from one node of a first group identified in the trigger frame and data from one node (separate from the first one) of a second and separate group identified in the trigger frame. A single access by the AP to the medium is thus required, reducing the channel occupation due to control frames. In some embodiments, the number of trigger frames can be drastically reduce, while offering resource units to several BSSs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/081,399, filed on Aug. 30, 2018, which is the National Phaseapplication of PCT Application No. PCT/EP2017/055490, filed on Mar. 8,2017, which claims the benefit under 35 U.S.C. § 119(a)-(d) of UnitedKingdom Patent Application No. 1604208.7, filed on Mar. 11, 2016 andentitled “IMPROVED ACCESS TO RANDOM RESOURCE UNITS BY A PLURALITY OFBSSs”. The above cited patent applications are incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to communication networks andmore specifically to the sending of data over a communication channelwhich is split into sub-channels (or Resource Units) that are availableto groups of nodes associated with a respective plurality of networkcells.

The invention finds application in wireless communication networks, inparticular to the access of an 802.11ax composite channel and of OFDMAResource Units forming for instance an 802.11ax composite channel forUplink communication. One application of the method regards wirelessdata communication over a wireless communication network using CarrierSense Multiple Access with Collision Avoidance (CSMA/CA), the networkbeing accessible by a plurality of node devices.

BACKGROUND OF THE INVENTION

The IEEE 802.11 MAC standard defines the way Wireless local areanetworks (WLANs) must work at the physical and medium access control(MAC) level. Typically, the 802.11 MAC (Medium Access Control) operatingmode implements the well-known Distributed Coordination Function (DCF)which relies on a contention-based mechanism based on the so-called“Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA)technique.

The 802.11 medium access protocol standard or operating mode is mainlydirected to the management of communication nodes waiting for thewireless medium to become idle so as to try to access to the wirelessmedium.

The network operating mode defined by the IEEE 802.11 ac standardprovides very high throughput (VHT) by, among other means, moving fromthe 2.4GHz band which is deemed to be highly susceptible to interferenceto the 5GHz band, thereby allowing for wider frequency contiguouschannels of 80 MHz to be used, two of which may optionally be combinedto get a 160 MHz channel as operating band of the wireless network.

The 802.11ac standard also tweaks control frames such as theRequest-To-Send (RTS) and Clear-To-Send (CTS) frames to allow forcomposite channels of varying and predefined bandwidths of 20, 40 or 80MHz, the composite channels being made of one or more channels that arecontiguous within the operating band. The 160 MHz composite channel ispossible by the combination of two 80 MHz composite channels within the160 MHz operating band. The control frames specify the channel width(bandwidth) for the targeted composite channel.

A composite channel therefore consists of a primary channel on which agiven node performs EDCA backoff procedure to access the medium, and ofat least one secondary channel, of for example 20 MHz each.

The primary channel is used by the communication nodes to sense whetheror not the channel is idle, and the primary channel can be extendedusing the secondary channel or channels to form a composite channel.

Given a tree breakdown of the operating band into elementary 20 MHzchannels, some secondary channels are named tertiary or quaternarychannels.

In 802.11ac, all the transmissions, and thus the possible compositechannels, include the primary channel. This is because the nodes performfull Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) andNetwork Allocation Vector (NAV) tracking on the primary channel only.The other channels are assigned as secondary channels, on which thenodes have only capability of CCA (clear channel assessment), i.e.detection of an idle or busy state/status of said secondary channel.

An issue with the use of composite channels as defined in the 802.11n or802.11ac (or 802.11ax) is that the 802.11n and 802.11ac-compliant nodes(i.e. HT nodes standing for High Throughput nodes) and the other legacynodes (i.e. non-HT nodes compliant only with for instance 802.11a/b/g)have to co-exist within the same wireless network and thus have to sharethe 20 MHz channels.

To cope with this issue, the 802.11n and 802.11ac standards provide thepossibility to duplicate control frames (e.g. RTS/CTS or CTS-to-Self orACK frames to acknowledge correct or erroneous reception of the sentdata) on each 20 MHz channel in an 802.11 a legacy format (called as“non-HT”) to establish a protection of the requested TXOP (transmissionopportunity) over the whole composite channel.

This is for any legacy 802.11a node that uses any of the 20 MHz channelinvolved in the composite channel to be aware of on-going communicationson the 20 MHz channel. As a result, the legacy node is prevented frominitiating a new transmission until the end of the current compositechannel TXOP granted to an 802.11 n/ac node.

As originally proposed by 802.11n, a duplication of conventional 802.11aor “non-HT” transmission is provided to allow the two identical 20 MHznon-HT control frames to be sent simultaneously on both the primary andsecondary channels forming the used composite channel.

This approach has been widened for 802.11ac to allow duplication overthe channels forming an 80 MHz or 160 MHz composite channel. In theremainder of the present document, the “duplicated non-HT frame” or“duplicated non-HT control frame” or “duplicated control frame” meansthat the node device duplicates the conventional or “non-HT”transmission of a given control frame over secondary 20 MHz channel(s)of the (40 MHz 80 MHz or 160 MHz) operating band.

In practice, to request a composite channel (equal to or greater than 40MHz) for a new TXOP, an 802.11n/ac node does an EDCA backoff procedurein the primary 20 MHz channel as mentioned above. In parallel, itperforms a channel sensing mechanism, such as a Clear-Channel-Assessment(CCA) signal detection, on the secondary channels to detect thesecondary channel or channels that are idle (channel state/status is“idle”) during a PIFS interval before the start of the new TXOP (i.e.before any queue backoff counter expires).

More recently, Institute of Electrical and Electronics Engineers (IEEE)officially approved the 802.11ax task group, as the successor of802.11ac. The primary goal of the 802.11ax task group consists inseeking for an improvement in data speed to wireless communicatingdevices used in dense deployment scenarios.

Recent developments in the 802.11ax standard sought to optimize usage ofthe composite channel by multiple nodes in a wireless network having anaccess point (AP). Indeed, typical contents have important amount ofdata, for instance related to high-definition audio-visual real-time andinteractive content. Furthermore, it is well-known that the performanceof the CSMA/CA protocol used in the IEEE 802.11 standard deterioratesrapidly as the number of nodes and the amount of traffic increase, i.e.in dense WLAN scenarios.

In this context, multi-user transmission has been considered to allowmultiple simultaneous transmissions to/from different users in bothdownlink and uplink directions. In the uplink to the AP, multi-usertransmissions can be used to mitigate the collision probability byallowing multiple nodes to simultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel into sub-channels, also referred to asresource units (RUs), that are shared in the frequency domain bymultiple users, based for instance on Orthogonal Frequency DivisionMultiple Access (OFDMA) technique. Each RU may be defined by a number oftones, the 20 MHz channel containing up to 242 usable tones.

OFDMA is a multi-user variation of OFDM which has emerged as a new keytechnology to improve efficiency in advanced infrastructure-basedwireless networks. It combines OFDM on the physical layer with FrequencyDivision Multiple Access (FDMA) on the MAC layer, allowing differentsubcarriers to be assigned to different nodes in order to increaseconcurrency. Adjacent sub-carriers often experience similar channelconditions and are thus grouped to sub-channels: an OFDMA sub-channel orRU is thus a set of sub-carriers.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

As currently envisaged, the granularity of such OFDMA sub-channels isfiner than the original 20 MHz channel band. Typically, a 2 MHz or 5 MHzsub-channel may be contemplated as a minimal width, therefore definingfor instance 9 sub-channels or resource units within a single 20 MHzchannel.

To support multi-user uplink, i.e. uplink transmission to the 802.11axaccess point (AP) during the granted TxOP, the 802.11ax AP has toprovide signalling information for the legacy nodes (non-802.11ax nodes)to set their NAV and for the 802.11ax nodes to determine the allocationof the resource units RUs.

It has been proposed for the AP to send a trigger frame (TF) to the802.11 ax nodes to trigger uplink communications. The trigger frame isadditional to other control (or signaling) messages sent by the AP, suchbeacon frames or probe messages defined in 802.11 ax.

As widely known, the control frame stream is detrimental to networkefficiency, in particular because, compared to exchange data, itsbitrate is reduced. Thus its transmission time duration is longer than asame-sized data message.

The document IEEE 802.11-15/0365 proposes that a ‘Trigger’ frame (TF) issent by the AP to solicit the transmission of uplink (UL) Multi-User(OFDMA) PPDU from multiple nodes. In response, the nodes transmit UL MU(OFDMA) PPDU as immediate responses to the Trigger frame. Alltransmitting nodes can send data at the same time, but using disjointsets of RUs (i.e. of frequencies in the OFDMA scheme), resulting intransmissions with less interference.

The bandwidth or width of the targeted composite channel is signalled inthe TF frame, meaning that the 20, 40, 80 or 160 MHz value is added. TheTF frame is sent over the primary 20 MHz channel and duplicated(replicated) on each other 20 MHz channels forming the targetedcomposite channel, if appropriate. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF frame. This preventsthese legacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

A resource unit RU can be reserved for a specific node, in which casethe AP indicates, in the TF, the node to which the RU is reserved. SuchRU is called Scheduled RU. The indicated node does not need to performcontention on accessing a scheduled RU reserved to it.

In order to better improve the efficiency of the system in regards toun-managed traffic to the AP (for example, uplink management frames fromassociated nodes, unassociated nodes intending to reach an AP, or simplyunmanaged data traffic), the document IEEE 802.11-15/0604 proposes a newtrigger frame (TF-R) above the previous UL MU procedure, allowing randomaccess onto the OFDMA TXOP. In other words, the resource unit RU can berandomly accessed by more than one node (of the group of nodesregistered with the AP). Such RU is called Random RU and is indicated assuch in the TF. Random RUs may serve as a basis for contention betweennodes willing to access the communication medium for sending data.

The above is introduced with respect to a single group of nodes that ismanaged by the access point with which each node has previouslyregistered. In the 802.11 standard, such a group of nodes together withthe access point is known as a Basic Service Set (BSS). The access pointacts as a master to control the nodes within the BSS. The simplest BSSconsists of one access point and one node.

Each BSS is uniquely identified by a specific basic service setidentification, BSSID. For a BSS operating in infrastructure mode, thespecific BSSID is usually a 48-bit MAC address of the access point. Thespecific BSSID is the formal name of the BSS and is always associatedwith only one BSS.

Together with the specific BSSID, each BSS has its own service setidentification, SSID, which is the informal (human) name of the BSS(since this own SSID identifier is often entered into devices manuallyby a human user).

In a BSS, the nodes usually contend for access to the communicationmedium as described above.

Recent developments provide that a single physical AP can operate as themaster nodes of a plurality of BSSs, i.e. of a plurality of independentgroups of nodes. This avoids using one physical AP per BSS or WLAN. Italso makes it possible to use the same primary channel for all BSSs,thereby avoiding channel interference problems.

Such operating scheme where a plurality of BSSs is managed by the samephysical AP is performed through so-called virtual access points(virtual APs or VAPs).

A Virtual AP is a logical entity that resides within a physical AccessPoint (AP). To a client, the VAP appears as an independent access pointwith its own unique SSID. To implement virtual APs, multiple BSSIDs areused with associated SSIDs. The BSSIDs for the VAPs in the physical APare usually generated from a base BSSID specific to the underlyingphysical AP, usually the base MAC address of the AP.

The terms Virtual AP, specific BSSID, BSS and SSID can be usedsynonymously throughout this document, to designate a group or cell ofnodes managed by a physical AP.

Depending on the context, specific BSSID and own SSID may further referto the identifier of a BSS/WLAN, either through a MAC address (specificBSSID) or an informal (human) name (own SSID).

Providing a plurality of SSIDs (or BSS) corresponds to providing variousdifferent networks in a particular area. It can give access to differentresources and present services which may have differing management orsecurity policies applied. This advantageously allows various categoriesof user, e.g. staff, students or visitors etc. to be provided withnetwork services which are appropriate to them.

In conventional 802.11 approaches, only one SSID (or BSS) is advertisedper signaling message such as a beacon frame. As a consequence, multiplebeacons are used to advertise the SSIDs corresponding to the virtual APsconfigured at the physical AP. This solution is compatible with most802.11 nodes and also allows the SSIDs to support different capabilitysets.

However, as the number of BSSs increases, more channel utilizationresults from such signaling. This downside is further increased becausethe signaling messages are transmitted at low bit rate, usually at thelowest supported data rate so that all clients can receive it.

In practice, each VAP sends a beacon frame every 100 ms.

To improve this situation of increased channel utilization in case ofmultiple BSSs, the IEEE 802.11v Wireless Network Managementspecification defines a mechanism to advertise multiple securityprofiles including BSSID/SSID advertisements, with a single beaconframe. This improvement is under consideration to be included in the802.11ax draft. However, the resulting network management is notsatisfactory. In particular, the medium access for each BSS (forinstance for uplink communication through trigger frames) is madeindependently of the other BSS. As a consequence, as the number of BSSsoperating on a given channel increases, so does the amount of contentionfor data frames.

SUMMARY OF INVENTION

It is a broad objective of the present invention to improve thissituation, i.e. to overcome some or all of the foregoing limitations. Itis thus sought to provide an improved access to resource units in an802.11 channel in case of multiple wireless networks (BSSs), inparticular for uplink transmission in 802.11.

In this context, embodiments of the invention provide, from the accesspoint's perspective, a wireless communication method in a wirelessnetwork comprising a physical access point and a plurality of nodesorganized into groups (BSSs), each group being managed by a virtualaccess point implemented in the physical access point, the methodcomprising the following steps, at the physical access point:

sending one trigger frame on the wireless network to reserve atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that the nodes access totransmit data during the reserved transmission opportunity, the triggerframe identifying a plurality of groups, nodes of which are allowed(only) to access the resources units to transmit data; and

in response to the trigger frame, receiving, over the resource unitsduring the reserved transmission opportunity, data from one node of afirst group identified in the trigger frame and data from one node(separate from the first one) of a second and separate group identifiedin the trigger frame.

From any node's perspective, these embodiments of the invention providea wireless communication method in a wireless network comprising aphysical access point and a plurality of nodes organized into groups(BSSs), each group being managed by a virtual access point implementedin the physical access point, the method comprising the following steps,at one node belonging to a first group:

receiving a trigger frame from the physical access point over thewireless network, the trigger frame reserving a transmission opportunityon at least one communication channel of the wireless network, thetransmission opportunity including resource units that form thecommunication channel and that the nodes access to transmit data duringthe reserved transmission opportunity, the trigger frame identifying aplurality of groups, nodes of which are allowed (only) to access theresources units to transmit data;

determining whether said first group to which the node belongscorresponds to one of the groups identified in the received triggerframe or not; and

only in case of positive determining, accessing at least one of theresource units during the transmission opportunity and transmitting dataover the accessed resource unit to the physical access point.

Thanks to the invention, the nodes of various BSSs may transmit data(e.g. uplink to the AP) during the same reserved TxOP. A consequence isthat the cost of the signaling (through trigger frames) is reduced, asthe contention for the various BSSs is made only once.

This is achieved by the invention through the indication of a pluralityof groups in the trigger frame used to contend for access the network.Indeed, the nodes of those groups are thus allowed to access theresource units provided during the reserved transmission opportunity.

Correlatively, the invention provides a communication device acting as aphysical access point in a wireless network also comprising a pluralityof nodes organized into groups (BSSs), each group being managed by avirtual access point implemented in the physical access point, thecommunication device acting as a physical access point comprising atleast one microprocessor configured for carrying out the steps of:

sending one trigger frame on the wireless network to reserve atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that the nodes access totransmit data during the reserved transmission opportunity, the triggerframe identifying a plurality of groups, nodes of which are allowed(only) to access the resources units to transmit data; and

in response to the trigger frame, receiving, over the resource unitsduring the reserved transmission opportunity, data from one node of afirst group identified in the trigger frame and data from one node(separate from the first one) of a second and separate group identifiedin the trigger frame.

From the node's perspective, the invention also provides a communicationdevice in a wireless network comprising a physical access point and aplurality of nodes organized into groups (BSSs), each group beingmanaged by a virtual access point implemented in the physical accesspoint, the communication device being one node belonging to a first oneof the groups and comprising at least one microprocessor configured forcarrying out the steps of:

receiving a trigger frame from the physical access point over thewireless network, the trigger frame reserving a transmission opportunityon at least one communication channel of the wireless network, thetransmission opportunity including resource units that form thecommunication channel and that the nodes access to transmit data duringthe reserved transmission opportunity, the trigger frame identifying aplurality of groups, nodes of which are allowed (only) to access theresources units to transmit data;

determining whether said first group to which the node belongscorresponds to one of the groups identified in the received triggerframe or not; and

only in case of positive determining, accessing at least one of theresource units during the transmission opportunity and transmitting dataover the accessed resource unit to the physical access point.

Optional features of embodiments of the invention are defined in theappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into system featuresdedicated to any node device according to embodiments of the invention.

In embodiments where each group is uniquely identified by a specificbasic service set identification, BSSID, derived from a base BSSIDspecific to the physical access point, the sent trigger frame includesthe base BSSID, thus identifying the plurality of groups managed by thephysical access point. From the node's perspective, the determining stepincludes comparing a BSSID included in the trigger frame with the baseBSSID. This approach makes it possible for the AP to easily identify allthe nodes it manages, while keeping compliance with the conventionalfields in the header frame. Indeed, as the base BSSID may be a MACaddress, it is compliant with the format of any address field in theheader frame. Thus, the base BSSID may be specified in a transmitter orreceiver address field in a header of the trigger frame.

Note that the base BSSID can be the base BSSID as defined in IEEE802.11v(48-bit MAC address of the physical AP known by all the nodes managed bythe AP) or the modified base BSSID in which n LSBs are set to zero (nbeing a parameter defining for instance the maximum number of BSSs).Indeed, the modified base BSSID corresponds to an intermediary stateduring the derivation process deriving the base BSSID to obtain thespecific BSSIDs for the BSSs. The modified base BSSID can thus also beseen as a base BSSID.

Of course, variants to the use of the base BSSID may be used, forinstance an explicit list of specific BSSIDs. In some cases, thesevariants may require adapting the format of the trigger frame to mirrorthe format of how the plurality of groups is defined in the triggerframe. Also, the trigger frame may include a BSSID field to receive aBSSID, the BSSID field being made of bits, at least one bit of whichdefining whether the received BSSID is specific BSSID of a specificgroup of nodes or a multiple-BSS address. For instance, the base BSSID(indicated in the trigger frame) is a 48-bit MAC address of the physicalaccess point, address in which at least one bit defines the receivedBSSID is a multiple-BSS address.

In alternative embodiments, the trigger frame includes (e.g. in additionto transmitter and receiver address fields defined below) at least onemulti-BSS field, the multi-BSS field indicating whether the transmissionopportunity provides resources units accessible by nodes of a pluralityof groups to transmit data, or not. In other words, the multi-BSS fieldmakes it possible to know whether or not the plurality of groups isdefined in the trigger frame. One may see that in the embodiment abovewhere the modified base BSSID (n LSBs are set to zero) is used, the nLSBs can be considered as a multi-BSS field. This is because all thepossible specific BSSIDs cannot have their n LSBs set to zero.

According to a specific feature, each group is uniquely identified by aspecific basic service set identification, BSSID, derived from a baseBSSID specific to the physical access point, and the sent trigger frameincludes a specific BSSID corresponding to a virtual access pointsending the trigger frame. As explained below, the knowledge of thederivation process makes it possible to know, from the specific BSSID,which BSSs are identified by the trigger frame.

For a given node, it requires reading, from the received trigger frame,a multi-BSS field to determine whether the transmission opportunityprovides resources units accessible by nodes of a plurality of groups totransmit data, or not. Thanks to this specific field, the node mayquickly determine whether a current transmission opportunity isdedicated to a plurality of BSSs, including its own group.

According to another specific feature, each group is uniquely identifiedby a specific basic service set identification, BSSID, derived from abase BSSID specific to the physical access point, and the determiningstep includes reading a specific BSSID from the trigger frame,bit-masking the read specific BSSID, and comparing the masking result toa specific BSSID of the first group. A specific use of this approach isfor the BSSID derivation process in which only the n LSBs of the baseBSSID are modified. In that case the bit-masking may be performed on the48-n MSBs between the read specific BSSID and the BSSID of the firstgroup (the group to which the current node belongs). Indeed, thespecific BSSIDs must have the same MSBs, due to the derivation process.Thus, if the bit-masking shows that the read specific BSSID and theBSSID of the first group have the same MSBs, the current node isconcerned (the determining is positive).

In some embodiments from the node's perspective, in case of negativedetermining, the node does not access any resource unit during thereserved transmission opportunity. This is because the node belongs to agroup which is not concerned by the received trigger frame. Usually, asthe node is not an addressee of the trigger frame, it sets its NAV to aduration value specified in the trigger frame, and waits for thisduration (i.e. duration of the transmission opportunity) before tryingto start again a contention mechanism for accessing the communicationchannel.

In embodiments, the trigger frame includes a cascading field to indicatethe reserved transmission opportunity is split into a plurality ofsuccessive time slots, each time slot providing resource units that thenodes access to transmit data. Thus, the node performs the followingstep: reading a cascading field in the trigger frame to determinewhether the reserved transmission opportunity is split into a pluralityof successive time slots or not, each time slot providing resource unitsthat the nodes access to transmit data.

It is thus avoided for the AP to contend again for a new access to thechannel in order to provide a new transmission time slot. As aconsequence, one or more PIFS are avoided, and channel occupation due tosignaling is substantially reduced.

Note that time slots define a time period during which each resourceunit is accessed by a single node to transmit data. The time slots areseparated one from the other by an interframe space (e.g. SIFS) andpossibly by acknowledgment messages from the access point.

In first embodiments of the invention, the physical access point sends atrigger frame before each time slot to announce the time slot withassociated resource units to the nodes. Thus the node performs thefollowing step: receiving, from the physical access point and beforeeach time slot, a trigger frame announcing the time slot with associatedresource units.

Such trigger frames thus synchronize the nodes that are about totransmit on the various resource units.

Each time slot preceded by a trigger frame may thus be assigned to agiven BSS. In that case for instance, each group is uniquely identifiedby a specific basic service set identification, BSSID, derived from abase BSSID specific to the physical access point and each trigger framesent by the AP includes, in addition to the base BSSID to define theplurality of groups, one specific BSSID corresponding to a group ofnodes to which the following time slot and associated resource units arereserved. Of course, a common BSSID value defining the plurality ofBSSIDs may be used instead of the base BSSID, in addition to thespecific BSSID.

This actually performs the assignment of a given time slot to a specificBSS. Thus, the node may perform the following steps: determining whetherone of the trigger frames received during the reserved transmissionopportunity includes, in addition to the base BSSID, a specific BSSIDcorresponding to the first group, or not;

and in case of positive determining, accessing at least one resourceunit of the time slot following the determined trigger frame andtransmitting data over the accessed resource unit to the physical accesspoint.

In specific embodiments, the base BSSID and the specific BSSID arespecified in one and the other of transmitter and receiver addressfields in a header of the trigger frame, requiring that, from the node'sperspective, the base BSSID and the specific BSSID are read fromtransmitter and receiver address fields in a header of the triggerframe.

These first embodiments advantageously keep compliancy with the TFformat as currently defined in the 802.11 standard.

In second embodiments of the invention, the trigger frame includes alist of BSSIDs defining to which groups of nodes the successive timeslots and associated resource units are respectively reserved. TheBSSIDs are usually specific BSSIDs corresponding to respective groups ofnodes (BSSs). However, a base or common BSSID corresponding to aplurality of groups can also be used in case it is desired to keep atime slot open to more nodes, for instance to all the nodes managed bythe AP. Such approach is described with more details below.

From the node's perspective, this requires the following steps:

reading a list of BSSIDs from the trigger frame;

determining, based on the read list of BSSIDs, one of the time slotsthat is at least reserved to the first group (indeed a time slot may bereserved for a plurality of groups);

accessing at least one resource unit of the determined time slot andtransmitting data over the accessed resource unit to the physical accesspoint.

The second embodiments further decrease the cost of signaling, sincetrigger frames are no longer made necessary to offer a plurality of timeslots with RUs to the nodes of different BSSs. As a consequence, channeloccupation due to signaling is substantially reduced.

In some specific embodiments, an acknowledgment, sent by the physicalaccess point, of data transmitted by nodes in a previous time slottriggers the start of a next time slot during the reserved transmissionopportunity. Specific to the time slot the node may access, it meansthat the start of the determined time slot is triggered by anacknowledgment, sent by the physical access point, of data transmittedby nodes in a previous time slot during the reserved transmissionopportunity. Note that the first time slot in the reserved transmissionopportunity is, of course, triggered by the sent/received trigger frame.

According to a specific feature, the next time slot starts after apredefined time period (e.g. a SIFS) after the transmission of theacknowledgment by the physical access point. From the node'sperspective, the determined time slot starts after a predefined timeperiod (.e.g. a SIFS) after the transmission of the acknowledgment bythe physical access point.

In third embodiments, that can be combined with the second embodimentsdefined above, the reserved transmission opportunity includes resourceunits that are accessed simultaneously by the nodes (e.g. throughOFDMA); and the trigger frame assigns at least a first resource unit anda second simultaneous resource unit to respectively a first group ofnodes and a second and distinct group of nodes. It means for the nodethat it further determines a subset of the simultaneous resources unitsthat is assigned to the first group to which the node belongs,

and in case the subset is not empty (it may be made of one or more RUs),it accesses at least one resource unit of the determined subset andtransmits data over the accessed resource unit to the physical accesspoint.

The third embodiments provide bandwidth assignment at RU level. A fineand precise assignment of the bandwidth resources to the various BSSscan thus be achieved.

In specific embodiments, the number of simultaneous resource unitsassigned to each group of nodes depends on use statistics of use ofresource units by each group in one or more previous transmissionopportunities. Thus, the AP is able to finely tune the bandwidthresources to the BSSs as the network conditions evolve, depending forinstance on which group needs bandwidth resources.

In embodiments, the trigger frame includes an indication of a durationof at least one timeslot within the reserved transmission opportunity todrive the nodes to end their transmissions during the at least onetimeslot at the same time.

As explained below, while the convention Duration Field of the triggerframe may be used to set the total duration of the reserved TXOP, the“HE-SIG-A Info” field also provided in a trigger frame may be used toset the time duration of a (each) specific time slot.

To achieve some of the embodiments of the invention, for instance thesecond or third embodiments above, the trigger frame may have a specificstructure, some examples of which are now described.

A multi-BSS field as described above may for instance be provided in thetrigger frame.

According to a specific feature, the node further determines, based onthe read multi-BSS field, a structure format of a per-BSS parametersection additional to transmitter and receiver address fields in thereceived trigger frame, a per-BSS parameter section defining anallocation of resource units to nodes of a single BSS. Indeed, differentparameters (and thus structural fields) may be required depending onwhether the multi BSS approach is used for the current transmissionopportunity.

In some embodiments, the trigger frame includes, in addition totransmitter and receiver address fields, a parameter section includingat least one cascading field, the cascading field indicating whether thetransmission opportunity includes a plurality of successive time slotsor not, each time slot providing resource units accessible by the nodesto transmit data.

Of course, the cascading field may be additional to the above multi-BSSfield.

In some other embodiments from the AP's perspective, the trigger frameincludes, in addition to transmitter and receiver address fields, aplurality of per-BSS parameter sections, at least current one(preferably each one) of the per-BSS parameter sections defining anallocation of resource units to nodes and including at least:

one BSSID field identifying one or more groups of nodes concerned by theallocation,

one timeslot field identifying a time slot concerned by the allocation,the reserved transmission opportunity being either made of one time slotor split into a plurality of time slots, each resource unit beingaccessed by a single node during a time slot to transmit data, one ormore RU usage fields, each RU usage field identifying one or moreresource units in the concerned time slot and one or more nodes of theconcerned group or groups authorized to access the one or moreidentified resource units. For instance, a wildcard value may be used toidentify and thus authorizing all the nodes of the concerned one or moregroups to access the identified resource units.

This approach requires for a specific node to: 1) read, within thereceived trigger frame, a plurality of per-BSS parameter sectionsadditional to transmitter and receiver address fields;

2) for at least one per-BSS parameter section defining an allocation ofresource units to nodes:

determine, based on one BSSID field included in the per-BSS parametersection, whether the first group is concerned by the allocation or not,determine, based on one timeslot field in the per-BSS parameter section,which time slot is concerned by the allocation, the reservedtransmission opportunity being either made of one time slot or splitinto a plurality of time slots, each resource unit being accessed by asingle node during a time slot to transmit data, and determine, based onone or more RU usage fields in the per-BSS parameter section, one ormore resource units in the concerned time slot and whether said node isauthorized to access the one or more determined resource units; and 3)in case the node is authorized to access the one or more determinedresource units, access at least one of the determining resource unitsduring the reserved transmission opportunity and transmit data over theaccessed resource unit to the physical access point.

This specific structure for the trigger frame is quite close to thecurrent format of the trigger frame, while allowing a very preciseallocation of the RUs to be performed.

In some specific embodiments, each group is uniquely identified by aspecific basic service set identification, BSSID, and a value in one ofthe BSSID fields is the specific BSSID of one group. Thus for the nodespecifically considered that accesses a resource unit, the read

BSSID field includes the specific BSSID of the first group. Thisprovision defines a resource allocation specific to a group of nodes.

In some variants, the specific BSSIDs of the groups derive from a baseBSSID specific to the physical access point and a value in the BSSIDfield is the base BSSID so that all the groups of nodes are concerned bythe allocation defined by the current per-BSS parameter section. For thenode, it means that the read BSSID field includes the base BSSID. Thisprovision defines a resource allocation open to all the nodes. This mayadvantageous be used when the AP desires to collect information from allthe nodes, for instance to gather buffer status or history, to allowregistration from nodes, etc. In that case, random resource units mayadvantageously be used since all the nodes can access them, depending onthe result of a contention scheme.

According to a specific feature, the BSSID field is n-bit long, where nis the number of bits varying between the specific BSSIDs compared tothe base BSSID. Reference to each group can be unambiguously made usingthe varying portion of their specific BSSIDs. This provision reduces thecost of indicating each specific BSSID in the trigger frame compared tothe use of conventional BSSIDs (48-bit long). Better usage of thenetwork bandwidth is thus obtained.

For instance, each group of nodes is associated with a n-bit BSS indexuniquely identifying the groups, and the BSSID field is n-bit longreceiving a n-bit BSS index associated with a specific group of nodes.

According to a variant, the BSSID field includes a bitmap, each bit inthe bitmap being associated with a respective group of nodes. Inaddition, if a node belonging to the first group accesses a resourceunit, it may mean that the bit (in the bitmap) associated with the firstgroup is enabled so that the first group is concerned by the allocation.

In some embodiments, the trigger frame defines at least one resourceunit that is accessible by any node from any one of two or more groups(preferably of all the groups). Such approach advantageously makes itpossible for the AP to offer bandwidth resources to all the nodes at thesame time, for instance to collect information from all the nodeswhatever the BSSs (for instance to gather buffer status or history, toallow registration from nodes, etc.). A specific node thus determines,from the trigger frame, that at least one resource unit is accessible byany node from any one of two or more groups; and accesses this resourceunit to transmit data to the physical access point.

To improve this situation, the trigger frame defines that all theresource units of at least one time slot are accessible by any node fromany one of two or more groups, the reserved transmission opportunitybeing either made of one time slot or split into a plurality of timeslots, each resource unit being accessible by a single node during atime slot to transmit data. From the node's perspective, it thusdetermines, from the trigger frame, that all the resource units of atleast one time slot are accessible by any node from any one of two ormore groups, the reserved transmission opportunity being either made ofone time slot or split into a plurality of time slots, each resourceunit being accessible by a single node during a time slot to transmitdata.

To further improve this situation, the trigger frame defines that allthe resource units in the reserved transmission opportunity areaccessible by any node from any one of two or more groups. From thenode's perspective, it thus determines, from the trigger frame, that allthe resource units in the reserved transmission opportunity areaccessible by any node from any one of two or more groups.

Another aspect of the invention relates to a wireless communicationsystem having a physical access point and at least one communicationdevice forming node as defined above.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a device of a communicationnetwork, causes the device to perform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the methods and node devices.

Another aspect of the invention relates to a wireless communicationmethod in a wireless network comprising a physical access point and aplurality of nodes organized into groups, substantially as hereindescribed with reference to, and as shown in, FIG. 8a , or FIG. 8b , orFIG. 8c , or FIG. 10 of the accompanying drawings.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a typical wireless communication system in whichembodiments of the invention may be implemented;

FIG. 2 illustrates 802.11ac channel allocation that support channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in the art;

FIG. 3 illustrates an example of 802.11ax uplink OFDMA transmissionscheme, wherein the AP issues a Trigger Frame for reserving atransmission opportunity of OFDMA sub-channels (resource units) on an 80MHz channel as known in the art;

FIG. 4 illustrates how an AP can poll two distinct BSSs using triggerframes;

FIGS. 5a, 5b and 5c present a first format of a Trigger frame;

FIG. 6 shows a schematic representation a communication device orstation in accordance with embodiments of the present invention;

FIG. 7 shows a schematic representation of a wireless communicationdevice in accordance with embodiments of the present invention;

FIGS. 8a, 8b and 8c illustrates exemplary embodiments of the inventionfor multiple BSS support with trigger Frame;

FIGS. 9a, 9b and 9c present a new format of a Trigger frame, adapted forimplementations of the invention; and

FIG. 10 illustrates, using a flowchart, general steps of a nodereceiving a Trigger Frame with multiple BSS support, according toembodiments of the invention.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

FIG. 1 illustrates a communication system in which several communicationnodes (or stations) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110. The radiotransmission channel 100 is defined by an operating frequency bandconstituted by a single channel or a plurality of channels forming acomposite channel.

Access to the shared radio medium to send data frames is based on theCSMA/CA technique, for sensing the carrier and avoiding collision byseparating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source or transmitting node first attempts through the physicalmechanism, to sense a medium that has been idle for at least one DIFS(standing for DCF InterFrame Spacing) time period, before transmittingdata frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source node continues to wait until the radio mediumbecomes idle.

To access the medium, the node starts a countdown backoff counterdesigned to expire after a number of timeslots, chosen randomly in thecontention window range [0, CW], CW (integer) being also referred to asthe Contention Window size and defining the upper boundary of thebackoff selection interval (contention window range). This backoffmechanism or procedure is the basis of the collision avoidance mechanismthat defers the transmission time for a random interval, thus reducingthe probability of collisions on the shared channel. After the backofftime period, the source node may send data or control frames if themedium is idle.

One problem of wireless data communications is that it is not possiblefor the source node to listen while sending, thus preventing the sourcenode from detecting data corruption due to channel fading orinterference or collision phenomena. A source node remains unaware ofthe corruption of the data frames sent and continues to transmit theframes unnecessarily, thus wasting access time.

The Collision Avoidance mechanism of CSMA/CA thus provides positiveacknowledgement (ACK) of the sent data frames by the receiving node ifthe frames are received with success, to notify the source node that nocorruption of the sent data frames occurred.

The ACK is transmitted at the end of reception of the data frame,immediately after a period of time called Short InterFrame Space (SIFS).

If the source node does not receive the ACK within a specified ACKtimeout or detects the transmission of a different frame on the channel,it may infer data frame loss. In that case, it generally reschedules theframe transmission according to the above-mentioned backoff procedure.

The wireless communication system of FIG. 1 comprises a physical accesspoint 110 configured to manage two or more WLANs (or BSSs), i.e. two ormore groups of nodes. Each BSS is uniquely identified by a specificbasic service set identification, BSSID and managed by a virtual APimplemented in the physical AP.

In the example shown, the physical AP implements two virtual APs,virtual AP 1 (100A) having MAC address MAC1 as specific BSSID to managea first WLAN (BSS), and virtual AP 2 (100B) having MAC address MAC2 asspecific BSSID to manage a second WLAN (BSS). Of course more WLANs canbe implemented, requiring a corresponding number of virtual APs to beimplemented in the physical AP.

All MAC addresses for the virtual APs are generated based on (or “derivefrom”) a base MAC address specific to the physical access point, usuallythe base 48-bit MAC address of AP 110. For instance MAC_(i) (‘i’ being aBSS index) used as specific BSSID(i) for virtual AP_(i) is generated asfollows, from the base MAC address BASE_BSSID:

$\left. {{MAC}_{i} = {{{BSSID}(i)} = \left. \left( {{BASE\_ BSSID}\mspace{14mu}{modified}\mspace{14mu}{to}\mspace{14mu}{set}\mspace{14mu}{the}\mspace{14mu} n\mspace{14mu}{LSBs}\mspace{14mu}{to}\mspace{14mu}{zero}} \right) \middle| {\left( {\left( {n\mspace{14mu}{LSBs}\mspace{14mu}{of}\mspace{14mu}{BASE\_ BSSID}} \right) + i} \right)\;{mod}\;{2\hat{}n}} \right.}} \right)$

where LSB refers to the least significant bits, “n” is an AP parameter(integer) defining the maximum number (about 2^(n)) of possible specificBSSIDs, and ‘|’ operator is an XOR operator. The specific BSSID(i) thusdiffer one from the other by their n LSBs. The 48-n MSBs of thegenerated specific BSSIDs are all similar to the corresponding bits ofBASE_BSSID.

As an example, virtual AP 1 provides a WLAN with “guest” as SSID thatone or more nodes can join, while virtual AP 2 provides a WLAN with“Employee” as SSID that other nodes can join simultaneously. Thesecurity for each WLAN is different, i.e. WEP and WPA. A same device canusually join two WLANs simultaneously if it has two separate WLANinterfaces (e.g. wifi network card). In that case, the device isconsidered as two nodes in the network, each node being able to joinonly one WLAN at a time.

Some control frames sent by the AP are an important part of 802.11, forinstance beacon frames and probe response frames. The nodes are waitingfor these frames to know about the WLANs or BSSs available.

These frames let the nodes know that an AP and one or more WLANs areavailable, but also notify the nodes about important information such asthe corresponding SSID or SSIDs, the corresponding specific BSSID orBSSIDs, the communication mode (Infrastructure or Ad-Hoc), theprotection security schemes used (e.g. Open, WEP, WPA-PSK or 802.1X),the support transmission rates used, the channel in operation andoptional Information Elements.

When multiple BSSs are provided, multiple beacons are transmitted by theAP, one for each active BSS, usually each 100 ms. It results in that thenodes have to process beacon frames more frequently and that channeloccupation due to control frames is increased (being noted that thecontrol frames such as the beacon frames are transmitted at low rate).

These drawbacks can be reduced by for example increasing the beaconinterval (more than 100 ms) so that the beacon frame of each BSS is sentless frequently. However, this may cause some nodes not to detect thebeacon frame of a given BSS when scanning, and thus to decide aparticular BSS (through its SSID) is not available.

To improve this situation, the IEEE 802.11v Wireless Network Managementspecification provides a mechanism to advertise multiple securityprofiles including BSSID advertisements. Thus, a single Beacon frame issent rather than multiple Beacon frames in order to advertise aplurality of specific BSSIDs/SSIDs. In this mechanism, a new InformationElement (IE) is defined (Multiple BSSID IE) in the beacon frames sent byone or the other of the multiple virtual APs (i.e. specific BSSIDs).

The transmitter address of such a beacon frame includes the specificBSSID of the transmitting virtual AP. Furthermore, the Multiple BSSID IEindicates that multiple BSSs is contemplated and provides an indicationof the maximum number of BSSs, parameter “n”, to the nodes, as well asthe common, inherited information element values of all of the BSSs(e.g. so that all members of the set use a common operating class,channel, channel access functions, etc.) and the unique informationelements of each of the other BSSs indexed by their BSSID indexes ‘i’(i.e. different advertised capabilities of the various BSSs, includingones from the BSS of the transmitting VAP).

As mentioned above, a BSSID index ‘i’ is a value between 1 and 2n-1,which identifies the BSSID. It may also be noted that the AP may includetwo or more Multiple BSSID elements containing elements for a givenBSSID index in one Beacon frame.

Such a multi BSS beacon frame may also transmit the base addressBASE_BSSID to the nodes.

To meet the ever-increasing demand for faster wireless networks tosupport bandwidth-intensive applications, 802.11ac is targeting largerbandwidth transmission through multi-channel operations. FIG. 2illustrates 802.11ac channel allocation that support composite channelbandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz

IEEE 802.11ac introduces support of a restricted number of predefinedsubsets of 20 MHz channels to form the sole predefined composite channelconfigurations that are available for reservation by any 802.11ac nodeon the wireless network to transmit data.

The predefined subsets are shown in the FIG. and correspond to 20 MHz,40 MHz, 80 MHz, and 160 MHz channel bandwidths, compared to only 20 MHzand 40 MHz supported by 802.11n. Indeed, the 20 MHz component channels200-1 to 200-8 are concatenated to form wider communication compositechannels.

In the 802.11ac standard, the channels of each predefined 40 MHz, 80 MHzor 160 MHz subset are contiguous within the operating frequency band,i.e. no hole (missing channel) in the composite channel as ordered inthe operating frequency band is allowed.

The 160 MHz channel bandwidth is composed of two 80 MHz channels thatmay or may not be frequency contiguous. The 80 MHz and 40 MHz channelsare respectively composed of two frequency adjacent or contiguous 40 MHzand 20 MHz channels, respectively. However the present invention mayhave embodiments with either composition of the channel bandwidth, i.e.including only contiguous channels or formed of non-contiguous channelswithin the operating band.

A node (including the AP) is granted a TxOP through the enhanceddistributed channel access (EDCA) mechanism on the “primary channel”(200-3). Indeed, for each composite channel having a bandwidth, 802.11acdesignates one channel as “primary” meaning that it is used forcontending for access to the composite channel. The primary 20 MHzchannel is common to all nodes (STAs) belonging to the same basic set,i.e. managed by or registered to the same local Access Point (AP).

However, to make sure that no other legacy node (i.e. not belonging tothe same set) uses the secondary channels, it is provided that thecontrol frames (e.g. RTS frame/CTS frame or trigger frame describedbelow) reserving the composite channel are duplicated over each 20 MHzchannel of such composite channel.

As addressed earlier, the IEEE 802.11ac standard enables up to four, oreven eight, 20 MHz channels to be bound. Because of the limited numberof channels (19 in the 5 GHz band in Europe), channel saturation becomesproblematic. Indeed, in densely populated areas, the 5 GHz band willsurely tend to saturate even with a 20 or 40 MHz bandwidth usage perWireless-LAN cell.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, one may consider multi-user transmission features,allowing multiple simultaneous transmissions to different users in bothdownlink and uplink directions, once a transmission opportunity has beenreserved. In the uplink, multi-user transmissions can be used tomitigate the collision probability by allowing multiple nodes tosimultaneously transmit.

To actually perform such multi-user transmission, it has been proposedto split a granted 20 MHz channel (200-1 to 200-4) into sub-channels 310(elementary sub-channels), also referred to as sub-carriers or resourceunits (RUs), that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique.

This is illustrated with reference to FIG. 3.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition within a reservedtransmission opportunity TXOP. This may help to reduce contention andcollisions inside 802.11 networks.

Contrary to downlink OFDMA wherein the AP can directly send multipledata to multiple stations (supported by specific indications inside thePLCP header), a trigger mechanism has been adopted for the AP to triggeruplink communications from various nodes.

To support an uplink multi-user transmission (during a pre-empted TxOP),the 802.11ax AP has to provide signalling information for both legacystations (non-802.11ax nodes) to set their NAV and for 802.11ax nodes todetermine the Resource Units allocation.

In the following description, the term legacy refers to non-802.11axnodes, meaning 802.11 nodes of previous technologies that do not supportOFDMA communications.

As shown in the example of FIG. 3, the AP sends a trigger frame (TF) 330to the targeted 802.11ax nodes to reserve a transmission opportunity.The bandwidth or width of the targeted composite channel for thetransmission opportunity is signalled in the TF frame, meaning that the20, 40, 80 or 160 MHz value is added. The TF frame is a control frame,according the 802.11 legacy non-HT format, and is sent over the primary20 MHz channel and duplicated (replicated) on each other 20 MHz channelsforming the targeted composite channel. As described above for theduplication of control frames, it is expected that every nearby legacynode (non-HT or 802.11ac nodes) receiving the TF on its primary channel,then sets its NAV to the value specified in the TF frame. This preventsthese legacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

Based on an AP's decision, the trigger frame TF may define a pluralityof resource units (RUs) 310, or “Random RUs”, which can be randomlyaccessed by the nodes of the network. In other words, Random RUsdesignated or allocated by the AP in the TF may serve as basis forcontention between nodes willing to access the communication medium forsending/uploading data during the reserved transmission opportunity. Acollision occurs when two or more nodes attempt to transmit at the sametime over the same RU.

A trigger frame that can be randomly accessed is referred to as atrigger frame for random access (TF-R). A TF-R may be emitted by the APto allow multiple nodes to perform UL MU (UpLink Multi-User) randomaccess to obtain an RU for their UL transmissions.

The trigger frame TF may also designate Scheduled resource units, inaddition or in replacement of the Random RUs. Scheduled RUs may bereserved by the AP for certain nodes in which case no contention foraccessing such RUs is needed for these nodes. Such RUs and theircorresponding scheduled nodes are indicated in the trigger frame. Forinstance, a node identifier, such as the Association ID (AID) assignedto each node upon registration, is added in association with eachScheduled RU in order to explicitly indicate the node that is allowed touse each Scheduled RU.

An AID equal to 0 may be used to identify random RUs.

The multi-user feature of OFDMA allows the AP to assign different RUs todifferent nodes in order to increase competition. This may help toreduce contention and collisions inside 802.11 networks.

In the example of FIG. 3, each 20 MHz channel (200-1, 200-2, 200-3 or200-4) is sub-divided in frequency domain into four sub-channels or RUs310, typically of size 5 Mhz.

Of course the number of RUs splitting a 20 MHz channel may be differentfrom four. For instance, between two to nine RUs may be provided (thuseach having a size between 10 MHz and about 2 MHz).

Once the nodes have used the RUs to transmit data to the AP, the APresponds with an acknowledgment frame (not show in the Figure) toacknowledge the data received. As for the other control frames, theacknowledgment frame is duplicated over each 20 MHz channel of suchcomposite channel. Preferably, the acknowledgment frame performs a blockacknowledgment, meaning that it acknowledges simultaneously reception ofdata transmitted over a plurality (e.g. all) of the RUs.

The trigger frame thus defines resource units including a plurality of(random and/or scheduled) resource units that the nodes can access. Ascurrently designed, a trigger frame is specific to a single BSS, meaningthat only the nodes belonging to that specific BSS are allowed to accessthe resource units included in the transmission opportunity reserved bythe trigger frame. For instance, the BSSID of the BSS considered (i.e.the MAC address of the virtual AP) is set in the transmitter addressfield of the header of the trigger frame.

FIG. 5a presents the MAC format of the trigger frame 330 according tothe 802.11 ax standard.

The Trigger frame is used to allocate (random and/or scheduled) resourceunits for UL MU transmission by 802.11 ax nodes. The trigger frame isduplicated in each 20 MHz of the targeted composite channel to reserve atransmission opportunity over the composite channel. The trigger framefollows the legacy format of control frames (no specific HT preamble).The TF 330 is made up of a MAC header and of additional fields. The MACheader includes the following fields common to all control frames: aframe control field 501, a duration field 502, a RA (Receiver Address)field 503, a TA (Transmitter Address) field 504. The additional fields,specific to the trigger frame, include a data portion formed ofinformation fields (510 and 520) specific to the TF, and a CRC/FCS(Cyclic Redundancy Check, or Frame Check Sequence, or also calledchecksum) field. The CRC/FCS field may optionally be preceded by apadding field of variable size (not shown in the figure), forconsiderations out of scope of the present invention.

The Duration field 502 is set to the estimated time, in microseconds,required for the pending uplink transmissions, and is used to set theNAV of nodes not targeted by the RA field 503. This Duration field 502thus sets the expected duration for the solicited transmissionopportunity TXOP.

The RA field 503 is set to the address of the recipient node or nodes.As a Trigger frame is intended for a group of nodes (a BSS), thestandard provides not specifying it at the time being to inferbroadcasting. The inventors propose, as an exemplary implementation, touse the wildcard MAC address (FF:FF:FF:FF:FF:FF) as a broadcastindication.

The TA field 504 is set to the address of the node transmitting theTrigger frame; it is typically the MAC address of the AP which sends theTF. When the AP hosts several virtual APs for multiple BSSs, the MACaddress of the current BSS (i.e. the specific BSSID or MAC address ofthe virtual AP concerned) is used for the TA field 504.

As the TF is dedicated to a single BSS, through the specifc BSSID set inthe TA field 504, the physical AP has to send successively a pluralityof trigger frames if it wants to provide respective transmissionopportunities (with resource units) to various BSSs.

FIG. 4 illustrates how the Access Point can poll two distinct BSSs. Thiscan be useful if the AP wants to successively query nodes of distinctBSSs for management matter (like buffer report).

The AP has to send two separate trigger frames for polling two BSSs.

The AP gains priority access to the communication medium (at least aftera PIFS time period with an idle medium, which is less than the DIFSduration necessary for the nodes managed by the AP to start a newcontention procedure), so that it can send a first TF to reserve a firsttransmission opportunity TXOP 1 for a first BSS, BSS 1. During TXOP 1,the nodes of BSS 1 can access the RUs and upload their data, while theAP acknowledges the reception thereof (ACK/BA in the FIG.).

Next, the AP relaxes the communication medium but immediately (afterPIFS) obtains priority again for access to the communication medium tosend another and second TF to reserve a second transmission opportunityTXOP 2 for a second BSS, BSS 2.

During TXOP 2, the nodes of BSS 2 can access the RUs and upload theirdata.

In the approach of FIG. 4, the wireless network comprising a physicalaccess point and a plurality of nodes organized into groups, each groupbeing managed by a virtual access point implemented in the physicalaccess point. The nodes contend for an access to the wireless network,and the contention process at each node starts or restarts once thewireless network is detected as idle for a predefined time period(usually DIFS time period after the end of a previous TXOP, for instanceafter an acknowledgment from the AP or after end of PPDU transmission).

The physical access point thus performs the step of sending a pluralityof trigger frames on the wireless network to reserve successivetransmission opportunities on at least one communication channel of thewireless network, each transmission opportunity being reserved for aspecific group of nodes and including resource units that form thecommunication channel and that the nodes of the specific group access totransmit data. Typically, a next trigger frame is sent after a timeperiod (e.g. PIFS) following a previous reserved transmissionopportunity, the time period being less that the predefined time period(defining nodes' contention for access to the network, e.g. DIFS).

During the time period (PIFS), the network is detected as idle becauseno node has restarted its contention mechanism and thus no node canaccess the network in the meantime.

Consequently, the physical access point receives, in response to eachtrigger frame and during the corresponding reserved transmissionopportunity, data from one or more nodes of the group specific to thetrigger frame.

One advantage of the approach of FIG. 4 is that the nodes perform aconventional processing.

The AP thus performs several TXOP reservations according to the numberof BSSs it wants to poll. Each reserved TXOP is independent from oneanother, in particular because the nodes not addressed by the triggerframe set their NAV to the Duration Field 502, and thus waits for thisduration.

The intention of the AP to send successive trigger frames using theabove priority (possibility to wait only a single first PIFS duration)may be specified in the trigger frame using a Cascade Indication, sothat the nodes not addressed by the first frame can listen to detect thesecond trigger frame. Nevertheless, this cascading is limited to nodesof a same BSS according to the current specification of the standard.

FIG. 5b illustrates Common Info field 510 forming part of the additionalfields in the TF 330.

It includes a Cascade Indication subfield 511 to indicate the successivetrigger frames. For instance, subfield 511 is to 0 when a subsequentTrigger frame will follow the current Trigger frame. Otherwise, theCascade Indication subfield is set to 0.

Common Info field 510 also includes a Trigger Type subfield 514 toindicate the type of the Trigger frame.

The other subfields in Common Info field 510 are of less importance forthe present invention (Length, HE-SIG-A Info, CP and LTF Type subfieldsindicate some parameters to format the HE trigger-based PPDU response,that is to say the uplink multi-user OFDMA frame).

FIG. 5c illustrates Per User Info field 520 also forming part of theadditional fields in the TF 330. The Per User Info field 520 defines theallocation of one or more resource units to nodes of the BSS addressedin TA field 504. A plurality of Per User Info fields 520 is usually usedto define the allocation of all the resource units of the transmissionopportunity.

User Identifier subfield 521 contains the 12 LSBs of the AssociationIDentifier (AID) of the node(s) to which the RU identified in RUAllocation field 522 is allocated, to transmit the MPDU(s) in the uplinkdirection.

The AID is a 16-bit unique value assigned to a node by the AP duringassociation handshake, i.e. during registration. The values other than1-2007 (0 and 2008-65535) are reserved, limiting the number of nodes foran AP to 2007. This is why using the 12 LSBs is sufficient. Inparticular, AID =0 is reserved for assigning the group of nodes formingthe BSS currently addressed (TA Field 504).

The AID management is performed per each virtual AP (i.e. per BSS).

As mentioned above, RU Allocation subfield 522 indicates the RU or RUsthat are allocated to the one or more nodes identified in UserIdentifier subfield 521. The length and coding of RU Allocation subfieldare not defined yet, but an index of ordered RUs may be used.

The other fields of Per User Info field 520 are of less importance forthe present invention.

The present invention seeks to provide a more efficient usage of thebandwidth in case of multiple BBSs.

The inventors have contemplated reducing the cost of signaling, inparticular regarding the trigger frames. To do so, they propose allowingnodes from various BSSs to be triggered for uplink communication, withina single channel access, i.e. during the same reserved transmissionopportunity.

Thanks to the use of a same transmission opportunity, trigger frames canbe avoided and/or any new trigger frame during the already reservedtransmission opportunity can be sent earlier. Thus occupation of thechannel due to the trigger frames is reduced and/or lost waiting timebefore sending a new trigger frame is also reduced.

Various embodiments are proposed below that all relate to a wirelesscommunication method in a wireless network comprising a physical accesspoint and a plurality of nodes organized into groups (BSSs), each groupbeing managed by a virtual access point implemented in the physicalaccess point and being uniquely identified by a specific basic serviceset identification, BSSID, the method comprising the following steps, atthe physical access point:

sending one trigger frame on the wireless network to reserve atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that the nodes access totransmit data during the reserved transmission opportunity, the triggerframe identifying a plurality of groups, nodes of which are allowed(only) to access the resources units to transmit data; and

in response to the trigger frame, receiving, over the resource unitsduring the reserved transmission opportunity, data from one node of afirst group identified in the trigger frame and data from one node(separate from the first one) of a second and separate group identifiedin the trigger frame.

Any node belonging to a group, called “first group”, and receiving suchtrigger frame thus determines whether said first group to which the nodebelongs corresponds to one of the groups identified in the receivedtrigger frame or not; and

only in case of positive determining, accesses at least one of theresource units during the transmission opportunity and transmits dataover the accessed resource unit to the physical access point.

FIG. 6 schematically illustrates a communication device 600, either anode 101-107 or the access point 110, of the radio network 100,configured to implement at least one embodiment of the presentinvention. The communication device 600 may preferably be a device suchas a micro-computer, a workstation or a light portable device. Thecommunication device 600 comprises a communication bus 613 to whichthere are preferably connected:

a central processing unit 611, such as a microprocessor, denoted CPU;

a read only memory 607, denoted ROM, for storing computer programs forimplementing the invention;

a random access memory 612, denoted RAM, for storing the executable codeof methods according to embodiments of the invention as well as theregisters adapted to record variables and parameters necessary forimplementing methods according to embodiments of the invention; and

at least one communication interface 602 connected to the radiocommunication network 100 over which digital data packets or frames orcontrol frames are transmitted, for example a wireless communicationnetwork according to the 802.11ax protocol. The frames are written froma FIFO sending memory in RAM 612 to the network interface fortransmission or are read from the network interface for reception andwriting into a FIFO receiving memory in RAM 612 under the control of asoftware application running in the CPU 611.

Optionally, the communication device 600 may also include the followingcomponents:

a data storage means 604 such as a hard disk, for storing computerprograms for implementing methods according to one or more embodimentsof the invention;

a disk drive 605 for a disk 606, the disk drive being adapted to readdata from the disk 606 or to write data onto said disk;

a screen 609 for displaying decoded data and/or serving as a graphicalinterface with the user, by means of a keyboard 610 or any otherpointing means.

The communication device 600 may be optionally connected to variousperipherals, such as for example a digital camera 608, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 600.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 600 or connected to it. The representation of thebus is not limiting and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 600 directly or by means of another element of the communicationdevice 600.

The disk 606 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to the invention to be implemented.

The executable code may optionally be stored either in read only memory607, on the hard disk 604 or on a removable digital medium such as forexample a disk 606 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 603, via the interface 602, in order to bestored in one of the storage means of the communication device 600, suchas the hard disk 604, before being executed.

The central processing unit 611 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 604 or in the read only memory 607, aretransferred into the random access memory 612, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 7 is a block diagram schematically illustrating the architecture ofthe communication device 600, either the AP 110 or one of nodes 100-107,adapted to carry out, at least partially, the invention. As illustrated,device 600 comprises a physical (PHY) layer block 703, a MAC layer block702, and an application layer block 701.

The PHY layer block 703 (here an 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancemedium access trigger frames TF 430 to reserve a transmission slot, MACdata and management frames based on a 20 MHz width to interact withlegacy 802.11 stations, as well as of MAC data frames of OFDMA typehaving smaller width than 20 MHz legacy (typically 2 or 5 MHz) to/fromthat radio medium.

The MAC layer block or controller 702 preferably comprises a MAC 802.11layer 704 implementing conventional 802.11ax MAC operations, and anadditional block 705 for carrying out, at least partially, theinvention. The MAC layer block 702 may optionally be implemented insoftware, which software is loaded into RAM 612 and executed by CPU 611.

Preferably, the additional block, referred as to multiple BSS managementmodule 705 for controlling access to OFDMA resource units (sub-channels)in case of multiple BBSs, implements the part of the invention thatregards device 600, i.e. transmitting operations for a source node,receiving operations for a receiving node, or operations for the AP.

For instance and not exhaustively, the operations for the AP may includegenerating and sending trigger frames as defined below, i.e. triggerframes identifying a plurality of groups, instead of a single BSS, toreserve a TXOP for multiple BSSs, and then managing the allocation ofresource units during the reserved TXOP to the nodes of the variousBSSs; the operations for a node different from the AP may includeanalyzing received trigger frames to determine if the node is allowed toaccess some resource units in the context the trigger frames allowseveral BSSs to communicate during the reserved TXOP.

MAC 802.11 layer 704 and multiple BSS management module 705 interact onewith the other in order to provide or process accurately trigger framesaccording to the invention.

On top of the FIG., application layer block 701 runs an application thatgenerates and receives data packets, for example data packets of a videostream. Application layer block 701 represents all the stack layersabove MAC layer according to ISO standardization.

Embodiments of the present invention are now illustrated using variousexemplary embodiments in the context of IEEE 802.11 ax by consideringOFDMA sub-channels. Although the proposed examples use the trigger frame330 (see FIG. 3) sent by an AP for a multi-user uplink transmissions,equivalent mechanisms can be used in a centralized or in an adhocenvironment (i.e. without an AP). Also the invention is not limited tothe 802.11ax context.

Below, the term legacy refers to non-802.11 ax nodes, meaning 802.11nodes of previous technologies that do not support OFDMA communications.

FIG. 8 illustrates, through timelines, three embodiments in which thenodes of various BSSs can communicate (upload data to AP) during thesame reserved TXOP, contrary to the timeline of FIG. 4.

The Trigger Frame is modified to identify a plurality of groups of nodesallowed to perform uplink OFDMA transmission in RUs.

In order that the Trigger Frame is received by all the nodes belongingto a plurality of BSS cells, embodiments provides that the sent triggerframe includes a base BSSID, BASE_BSSID, which is computed from (orsimilar to) the base 48-bit MAC address of the physical AP, thusidentifying the plurality of groups managed by the physical accesspoint. The base BSSID is seen as an AP address commonly known by allnodes managed by the physical AP. The base BSSID may be specified in theTA or RA field 503 or 504 in a header of the trigger frame. The baseBSSID is thus seen as a multi-BSS address.

As all the nodes know the base BSSID (which can be transmitted in orretrieved from the beacon frames), they are able to identify it in TA orRA field. Upon detecting the base BSSID, the nodes know they areconcerned by the reserved TXOP, thus starting to determine in which RUor RUs forming the TXOP they could transmit data (either throughcontention for random RUs or through direct access for scheduled RU).

The base BSSID may be the base MAC address of the AP, BASE_BSSID, or bethe BASE_BSSID modified to set the n LSBs to zero. This is because,given the scheme for generating the specific BSSIDs for the BSSs by theAP, all the specific BSSIDs have the same 48-n MSBs as BASE_BSSID. Thus,the modified BASE_BSSID is sufficient for the nodes to determine whetheror not their BSSs are concerned by the trigger frame. This approachclearly voids the n LSBs, so that the nodes can easily detect theircorresponding BSSID is concerned, by bit-masking on the other bits (the48-n MSBs).

In an alternative embodiment, a multi-BSS address to be used to identifythe plurality of groups may be a 48-bit MAC address based on BASE_BSSID(either BASE_BSSID itlsef of the modified BASE_BSSID with the n LSBs setto 0), wherein one bit, for instance bit #0 (usually called theIndividual/Group bit), is set to 1 to indicate it is a group address. Inthis alternative embodiment, only one bit needs to be tested in order todetermine whether the BSSID specified in the trigger frame indicates aplurality of BSSs.

These embodiments provide targeting all the BSSs managed by the samephysical AP since the base BSSID of the AP is used as “multi-BSSaddress” to indicate a plurality of BSSs. Of course, other embodimentsmay be used that identify a subset of all the AP-managed BSSs available.For instance, the TA or RA field used to define the plurality of BSSsmay be used as a 48-bit bitmap which associates each of its bits to agiven BSS (in increasing order for instance). It is contemplated that 48BSSs simultaneously managed by a single AP covers a large number ofsituations. Thus each bit set to 1 in the 48-bit bitmap indicates thatthe associated BSS is concerned by the TF.

In another alternative embodiment, a multi-BSS address to be used toidentify the plurality of groups may be any 48-bit MAC address of oneVAP (i.e. any specific BSSID), and the trigger frame format contains anexplicit information field for a multiple BSS indication (as furtherdescribed by field 912 of FIG. 9b ). In this embodiment, the triggerframe includes at least one multi-BSS field, the multi-BSS fieldindicating whether the transmission opportunity provides resources unitsaccessible by nodes of a plurality of groups to transmit data, or not;and each group being uniquely identified by a specific basic service setidentification, BSSID, derived from a base BSSID specific to thephysical access point, the sent trigger frame includes a specific BSSIDof a virtual access point sending the trigger frame.

FIGS. 8a and 8b illustrate respectively first and second embodiments inwhich a plurality of time slots is cascaded within the TXOP reserved bya first trigger frame. To be more precise, the trigger frame includes acascading field to indicate the reserved transmission opportunity issplit into a plurality of successive time slots, each time slotproviding resource units that the nodes access to transmit data. It maybe the Cascade Indication subfield 511 defined above. Thanks to thissubfield, any node receiving the trigger frame and concerned by thereserved TXOP is able to determine that successive time slots areprovided during the TXOP.

FIG. 8a illustrates the first embodiments in which conventional triggerframes are used, except for the use of a multi-BSS address (such asBASE_BSSID) in TA or RA field 503 or 504. It means that a series of TF330 is used in cascade in order to grant successively uplinkcommunications for each of the desired BSSs, within the TXOP reserved bythe very first TF.

In these first embodiments, the physical access point sends a triggerframe before each time slot to announce the time slot with associatedresource units to the nodes. As each time slot (and thus trigger frame)is dedicated to a single BSS, each trigger frame sent by the APincludes, in addition to the base BSSID to define the plurality of BSSsconcerned by the trigger frame, one specific BSSID corresponding to agroup of nodes to which the following time slot and associated resourceunits are reserved. It means that the nodes have to identify the timeslot (and thus trigger frame) dedicated to their BSS. To do so, theydetermine whether one of the trigger frames received during the reservedtransmission opportunity includes, in addition to the base BSSID, aspecific BSSID corresponding to their own group, or not;

and in case of positive determining, they access at least one resourceunit of the time slot following the determined trigger frame andtransmit data over the accessed resource unit to the physical accesspoint.

In an exemplary timeline with two BSSs as shown in FIG. 8a , TF 330-A isused for a first BSS, BSS_1, whereas TF 330-B deals with a second BBS,BSS_2.

After contention or PIFS period elapsed on the medium, the AP sends afirst trigger frame 330-A reserving TXOP. To address a plurality ofBSSs, the AP indicates BASE_BSSID (or equivalent multi-BSS address thatencompasses a plurality of BSSs) in TF 330-A. This indicates to all thenodes that nodes of two or more BSSs will have an opportunity (throughRUs) to transmit during TXOP.

The concerned nodes thus do not set their NAV. For the other nodes(other BSSs), the duration in Duration field 502 of the TF is set to anapproximate value covering all the duration of the TXOP (the later TF330-B will decrease and more finely tune the remaining duration).

In one embodiment, TA field 504 is set to identify the plurality of BSSsconcerned by the TXOP, either a list of BSSIDs or REF_BSSID as mentionedabove. RA field 503 is set to a specific BSSID value corresponding to asingle BSS that is allowed to communicate during the time slot 310-Afollowing TF 330-A. In the example of FIG. 8a , RA field 503 includesBSSID_1 in order to inform the nodes of BSS 1 that they will haveopportunities (RUs) to upload data.

In an alternative embodiment, the opposite scheme is implemented,wherein BASE_BSSID or the like to identify a plurality of BSSs is set inRA field 503 field to inform of the multiple BSS support, while aspecific BSSID is set in TA 504 to inform that the following time slotis allocated to the corresponding BSS.

TF 330-A has its Cascade Indication subfield 511 set to 1 to indicate aplurality of TFs (including itself) is expected. Since BASE_BSSID isindicated in the frame header, the plurality of TFs, and correspondingtransmission time slots, will be provided during the same TXOP reservedby the first TF.

If Cascade Indication subfield 511 is not set, meaning the reserved TXOPincludes only one BSS, there is no multiple BSS scheme. The nodes notconcerned by the unique TF 330 as indicated through the specific BSSIDspecified in TA or RA field may defer and set its NAV to the DurationField 502.

The nodes of BSS 1 can thus transmit data during time slot 310-A whenthey access the resource units, either through scheduled RUs or randomRUs (as specified in the Per User Info fields 520). The AP mayacknowledge (ACK/BA) the received data.

Note that the time length of timeslot 310-A may be defined in “HE-SIG-AInfo” field 512. This is because 802.11ax standard mandates the AP toset the value of the timeslot in this field 512. This field, thatconventionally defines the time duration for the whole TXOP, is now usedfor a subpart of the TXOP, namely each timeslot per BSS (UL MU PPDUduration per BSS).

Thanks to this “HE-SIG-A Info” field, the trigger frame may include anindication of a duration of at least one time slot within the reservedtransmission opportunity to drive the nodes to end their transmissionsduring the at least one time slot at the same time.

Next, after a SIFS duration (less than the PIFS duration of FIG. 4) theAP sends another trigger frame 330-B to provide another time slot for asecond BSS, BSS 2. TF 330-B thus includes BSSID_2 and BASE_BSSID (or thelike) in the TA and RA fields.

The AP may also refine the duration of TXOP through a new value in theDuration field 502.

As for the first time slot, the nodes of BSS 2 access the resource unitsforming 300-B to transmit data.

This scheme can be iterated any number of times to offer new uplinkcommunication time slots to the various BSSs.

Once a node has found its corresponding TF and has transmitted itsuplink data during 310, it may enter in doze mode for each successiveremaining TF, or may wait for a new TF specifying again the BSSID of itsown BSS during the reserved TXOP.

The above shows that, whatever the option selected for the base BSSIDand the specific BSSID to be specified in one and the other oftransmitter and receiver address fields in a header of the triggerframe, the usage of common BASE_BSSID (or the like) and specific BSSIDmakes it possible for the nodes to detect multiple BSS support and tolocate their assigned TF(s) and transmission time slot(s).

In a slight variant as introduced above, instead of using the baseBSSID, only the specific BSSID may be indicated in the trigger frame,together with a separate multi-BSS indication (912 discussed below forinstance). Bit-masking on the specific BSSID makes it possible for allthe nodes to determine whether they are concerned or not by the currentreserved TXOP, in case the multi-BSS indication is enabled.

The first embodiments reduce channel occupation duration because onlyone single medium access is performed and the next TF can be sent usingreduced mandatory PIFS interframe space given the priority of the AP dueto the reserved TXOP.

FIG. 8b illustrates the second embodiments in which a single initialtrigger frame is used to define the allocation of resource units in thesuccessive time slots forming the reserved TXOP.

In these second embodiments, the trigger frame includes a list of BSSIDsdefining to which groups of nodes the successive time slots andassociated resource units are respectively reserved. The list of BSSIDsmay be formed of a set of successive information fields in the triggerframe, each field defining a time slot allocation for one or moreBSSIDs.

Any node concerned by the received TF (because its BSS is included inthe set of BSSIDs indicated in the TF) can thus read the list of BSSIDsfrom the trigger frame; determine, based on the read list of BSSIDs, oneof the time slots that is at least reserved to its own group (a timeslot may be reserved for a plurality of groups, using for instance amulti-BSS address, such as REF_BSSID); and access at least one resourceunit of the determined time slot and transmit data over the accessedresource unit to the physical access point.

As shown in the exemplary timeline of FIG. 8b , one single TF 830 isused for directing UL MU transmission of several BSS successively. Toachieve that, TF 830 follows a new format, an example of which isdescribed below with reference to FIG. 9, in order to provide a list ofBSSIDs and inform that each BSSID is allowed to occur in cascadingscheme.

FIG. 9a illustrates the MAC format of trigger frame 830. The MAC headerportion is the same as TF 330 of 802.11ax standard shown in FIG. 5aabove. This is to keep compliancy with the MAC protocol. Thus, theBASE_BSSID (or the like to identify a plurality of BSSs) may be used inTA or RA field as explained above to indicate multiple BSS scheme.

In the case of FIG. 8b (and also 8 c described below), as the triggerframe is general for all the timeslots, the TA and RA fields are used atmost only to provide multi-BSS capability. As a result, the TA field 504may be set to BASE_BSSID (or the like) in order to advertise the nodesthat the TXOP follows a multiple BSS scheme. The RA field 503 is theaddress of the intended recipient nodes: either a wildcard address isused as a broadcast indication, or either BASE_BSSID is used again.

The payload of trigger frame 830 is also formed of one Common Info field910 that may slightly differ from field 510 and a series of Per BSS Infofields 920 which differ from fields 520 to define the allocation of thesuccessive time slots.

As shown in FIG. 9b , The “Common Info” field 910 has the same format as510, except that a new bit field, “multi BSS indication” 912, is addedto inform, as a double check, of the new format used by the triggerframe. Multi BSS indication 912 is set to 1 (enabled) if the requestedTXOP is dedicated to a group of BSSs; and set to 0 otherwise. Thus, thetrigger frame includes, in addition to transmitter and receiver addressfields, a parameter section including at least one multi-BSS field, themulti-BSS field indicating whether the transmission opportunity providesresources units accessible by nodes of a plurality of groups to transmitdata, or not.

However, the same information can be deduced from the use of BASE_BSSID(or the like as defined above) in TA or RA field 503 or 504 of MAC frameheader as described above. As a consequence, Common Info field 910 isoptional to explicitly declare the multiple BSS scheme, and conventionalCommon Info field 510 (i.e. without multi-BSS indication 912) may alsobe used in which case multiple BSS scheme is only declared through theuse of a multi-BSS address such as BASE_BSSID in the MAC header.

Of course, in case it is decided the BASE_BSSID or the like to identifythe plurality of BSSs is not specified in the MAC frame header,multi-BSS indication bit 912 becomes mandatory in order to detect themultiple BSS format of the TF. Common Info field 910 thus becomesmandatory instead of Common Info field 510.

Detection of multiple BSS scheme is required to distinguish between theformat of TF 330 and the format of TF 830.

The above shows that at least two means to allow determining if the nextfields follow conventional format 520 or format 920 as now described areprovided. As a consequence, by reading the multi-BSS field, a node candetermine a structure format of a per-BSS parameter section additionalto transmitter and receiver address fields in the received triggerframe.

FIG. 9c discloses an exemplary format of Per BSS Info field 920 thatgives BSS information for allocating time slots and resource units.Usually,

A plurality of per-BSS parameter sections, namely Per BSS Info fields920, is used in the trigger frame, at least current one (preferably eachone) of the per-BSS parameter sections defining an allocation ofresource units to nodes. The plurality of sections 920 makes it possibleto define the allocation of all the time slots forming the reservedTXOP.

BSS identifier field 921 is used to identify a specific BSS (through aspecific BSSID). It means the BSSID field identifies one specific groupof nodes concerned by the allocation.

BSS identifier field 921 may be a 6-byte address field, in order toreceive a full BSSID, which may for instance be the specific BSSID of aspecific BSS. In other words, a BSSID in at least one of the BSSIDfields is the specific BSSID of one group.

In variants, as the TF has already been successfully filtered by theTA/RA couple through the MAC header (including BASE_BSSID or the likeinformation), it is sufficient to only distinguish between the possiblespecific BSSIDs generated from BASE_BSSID. Thus a shorter identifier canbe used, for instance index (i) identifying the i^(th) BSSID within themultiple specific BSSIDs derived from the base BSSID (BASE_BSSID), wherei is less than 2^(n)−1. The BSSID field is thus n-bit long, where n isthe number of bits varying between the specific BSSIDs compared to thebase BSSID.

Given the indication provided in BSS identifier field 921, the pluralityof Per BSS Info fields 920 lists a cascade of BSSs.

TF Index Allocation field 922 is used in coordination with CascadeIndication field 511 to indicate the index of the timeslot concerned bythe allocation defined in the current Per BSS Info field 920. In otherwords, it defines the timeslot the BSS indicated in BSS identifier field921 will be allowed to use for uplink communication, The timeslots maybe indexed with an increasing numbering from the beginning of thereserved TXOP.

Fields 923 to 926 are common parameters of the current BSS, and areequivalent to parameters 523 to 526.

One or more RU Usage fields 927 are then provided.

RU Usage field 927 has the same function as Per User Info field 520 ofFIG. 5c , namely defining the allocation of the resource units formingthe timeslots identified in field 922 to the nodes belonging to the BSSidentified in field 921. A plurality of RU Usage fields 927 makes itpossible to define the allocation of each RU forming the timeslotsidentified in field 922. These fields are thus used to finely tune theRU usage per BSS (or per a given set of BSS if a bitmap is used in 921).

In the example shown in the Figure, two formats 950 and 520 areproposed.

Format 950 is the simplest format and comprises only two fields: UserIdentifier subfield 521 includes the Association IDentifier (AID) of thenode (belonging to the BSS identified in field 921) to which the RU orRUs identified in RU Allocation field 522 is/are allocated, to transmitthe MPDU(s) in the uplink direction. AID is set to 0 to define randomRUs; otherwise it is set to a specific node AID.

Format 520 reuses the entire format of “Per User Info Field” 520 definedabove.

Use of either format may be specified using a dedicated bit before theRU Usage fields 927.

Of course, the trigger frame may mix RU Usage fields 927 conforming toformat 920 and others conforming to format 520. In this case, use ofeither format may be specified using a dedicated bit before each RUUsage field 927.

Any node that wants to know which RU it can access thus has to:

1) read, within the received trigger frame, a plurality of per-BSSparameter sections 920 additional to transmitter and receiver addressfields 503, 504;

2) for at least one per-BSS parameter section 920 defining an allocationof resource units to nodes:

-   -   determine, based on one BSSID field 921 included in the per-BSS        parameter section, whether its own group is concerned by the        allocation or not,    -   determine, based on one timeslot field 922 in the per-BSS        parameter section, which time slot is concerned by the        allocation, the reserved transmission opportunity being either        made of one time slot or split into a plurality of time slots,        each resource unit being accessed by a single node during a time        slot to transmit data, and    -   determine, based on one or more RU usage fields 927 in the        per-BSS parameter section, one or more resource units in the        concerned time slot and whether said node is authorized to        access the one or more determined resource units.

Next, in case the node is authorized to access the one or moredetermined resource units, it accesses at least one of the determiningresource units during the reserved transmission opportunity andtransmits data over the accessed resource unit to the physical accesspoint.

Back to FIG. 8b , the trigger frame thus has two Per BSS Info fields920, the first one indicating the first timeslot 310-A (as example “1”in field 922) is allocated to BSS 1 field 921 set to BSSID_1), while thesecond one indicates the second timeslot 310-B (as example “2” in field922) is allocated to BSS 2 (field 921 set to BSSID_2),

Thus the nodes of BSS 1 access the RUs of 310-A according to the RUallocation defined in RU usage fields 927 of the first Per BSS Infofield 920, to transmit data to the AP. Once timeslot 310-A for uplinkends, the AP acknowledges reception of the data. As mentioned above, thetime length of timeslot 310-A may be defined in “HE-SIG-A Info” field512. As a plurality of timeslots is provided, the “HE-SIG-A Info” fieldmay be formed to define the successive time duration of each timeslot.

Next, after a SIFS, the second timeslot 310-B starts. It means that anacknowledgment, sent by the physical access point, of data transmittedby nodes in a previous time slot 310-A triggers the start of a next timeslot 310-B during the reserved transmission opportunity TXOP. And thenext time slot starts after a predefined time period (e.g. a SIFS) afterthe transmission of the acknowledgment by the physical access point. Theacknowledgment ACK/BA of the preceding transmission thus serves as asynchronization point for the next UL MU transmission of a next BSS.

It follows that the nodes of BSS 2 can access the RUs of 310-B accordingto the RU allocation defined in RU usage fields 927 of the second PerBSS Info field 920 (in the trigger frame), to transmit data to the AP.Once timeslot 310-B for uplink ends, the AP acknowledges reception ofthe data.

Of course, one understands that a larger number of timeslots can beprovided, that follow the mechanism as described above, to provide RUsfor successive BSSs.

As readily apparent from FIG. 8b , channel occupation due to controlframes, in particular due to the trigger frames, is substantiallyreduced compared to the first embodiments. This is because only a singleTF is sent that defines the allocation of RUs for a plurality ofsuccessive timeslots.

The second embodiments particularly provide high benefits in case ofhigh-loaded cells, i.e. where the total number of available RUs is notenough to fulfil the need of the at least two BSSs.

FIG. 8c illustrates the third embodiments in which a plurality of BSSsshares the simultaneous RUs of the same timeslot. Indeed, the reservedtransmission opportunity includes resource units that are accessedsimultaneously by the nodes (e.g. through OFDMA).

In these third embodiments, the trigger frame assigns at least a firstresource unit and a second simultaneous resource unit to respectively afirst group of nodes and a second and distinct group of nodes. Itrequires for each node concerned by the trigger frame to determine asubset of the simultaneous resources units that is assigned to its owngroup (BSS to which it belongs), and in case the subset is not empty (itmay be made of one or more RUs), to access at least one resource unit ofthe determined subset and transmit data over the accessed resource unitto the physical access point.

The trigger frame thus needs to define the allocation of simultaneousRUs to the various BSSs. Next the allocation of RUs to nodes within agiven BSS can follow the conventional scheme described above.

The format of TF as explained above with reference to FIGS. 9 can beused.

The general format of TF as shown in FIG. 9a and the format of CommonInfo field 910 of FIG. 9b are the same as above. Note that the CascadeIndication field 511 can be set to 0 in the case a single timeslot isprovided, as it is the case in FIG. 8c .

Regarding the Per BSS Info field 920 of FIG. 9c , it must be noted that,in the case of FIG. 8c , a single timeslot is provided. Thus TFAllocation field 922 is optional and can be absent (the rule is that ifCascade Indication field 511 is set to 0, there is no field 922). Thisis to save some bits and thus channel occupation. Of course, in avariant, TF Allocation field 922 can be kept in any case, and be set to1 (to designate the sole timeslot) in case of a single timeslot.

Still regarding the Per BSS Info field 920, the third embodimentsprovide that the same timeslot is shared between various BSSs. Thus, aplurality of Per BSS Info field 920 can be used, each one dedicated to asingle BSS (identified in BSS identifier field 921) but for the sametimeslot, and defining, through one or more RU Usage fields 927, theallocation to its nodes of RUs reserved for this BSS in the timeslot.

In the third embodiments, an AP managing several virtual-APs candynamically and finely tune the number of RUs per BSSID to occur inparallel (simultaneously).

As an example, if a BSS encounters a low number of nodes or mediumcontention (typically a “guest” network having poor utilization), thenthe AP may decide to allocate a limited number of RUs to this BSS, andprovide a higher number of RUs to another and denser BSS.

Sharing the simultaneous RUs of the same TXOP or timeslot betweenvarious BSSs thus makes it possible to avoid using specific triggerframes for low-used BSSs, which is very time and bandwith-consumingcompared to the limited need.

As a consequence, the AP may dynamically adjust the number of RUs toeach BSS, according to TXOP history. In other words, the number ofsimultaneous resource units assigned to each group of nodes (BSS) maydepend on use statistics of use of resource units by each group in oneor more previous transmission opportunities.

Fourth embodiments not shown in the Figures combine the second and thirdembodiments. It means that with a single trigger frame, a plurality ofsuccessive timeslots is defined, one or more of the timeslots providingsimultaneous RUs assigned to nodes of different BSSs. Preferably, allthe timeslots are shared between BSSs.

The Cascade Information field 511 is thus set to 1.

Fifth embodiments may apply to any of the second to fourth embodiments.

The fifth embodiments consist in letting some RUs or timeslots opened toaccess to a plurality of BSSs. In other words, there is no specificallocation provided to RUs. A consequence is that a pure random accessby two or more (preferably all the BSSs managed by the AP) is achieved.

This approach can be considered as an overall broadcast BSS, in order tocollect the overall needs (node management like registration, bufferstatus, etc.) of the BSSs managed by an AP.

Various degrees of this approach can be achieved.

At RU level, the trigger frame defines at least one resource unit thatis accessible by any node from any one of two or more BSSs. Beforeaccessing this resource unit, any node must check whether its own BSScorrespond to one of the two or more BSSs as specified.

At timeslot level, the trigger frame defines that all the resource unitsof at least one time slot are accessible by any node from any one of twoor more groups, the reserved transmission opportunity being either madeof one time slot or split into a plurality of time slots, each resourceunit being accessible by a single node during a time slot to transmitdata.

At TXOP level, the trigger frame defines that all the resource units inthe reserved transmission opportunity are accessible by any node fromany one of two or more groups.

The same format of TF as defined above with reference to FIGS. 9 can beused.

However, since one or more RUs are assigned to a plurality of BSSs, BSSidentifier field 921 can be used to indicate a plurality of BSSs(through a list of BSSIDs or using a multi-BSS address such asBASE_BSSID or using a bitmap). In that case it means the BSSID fieldidentifies a plurality of groups of nodes concerned by the allocation.

In case BSS identifier field 921 is a 6-byte address field, it candirectly receive BASE_BSSID or any multi-BSS address that identify agroup of BSSIDs or a 48-bit bitmap. In other words, a value in the BSSIDfield may be the base BSSID so that all the groups of nodes areconcerned by the allocation defined by the current per-BSS parametersection 920.

Instead of setting a BSSID identifying a plurality of groups of nodes,or a corresponding index, BSS identifier field 921 may receive a bitmapas briefly introduced above, each bit in the bitmap being associatedwith a respective group of nodes (according to an increasing numberingorder for instance, like a BSS index). This makes it possible to defineany group of BSSs. The BSS associated with each bit of the bitmap isknown by all the nodes, including the AP.

For instance, an 8-bit bitmap for 921 supports up to 8 BSSs. Longerbitmaps can be used to adapt to the number of BSSs simultaneouslymanaged by the physical AP.

The use of a bitmap advantageously allows a common configuration forseveral BSSs to be set in a single “Per BSS Info” field 920.

Any node receiving the trigger frame and belonging to a BSS concerned bythe TF will analyze the embedded Per BSS Info fields 920 to determinewhich field 920 defines a RU allocation for its BSS. To do so, it firstreads each bitmap in each Per BSS Info field 920 in order to determinewhether the bit associated with its own group is enabled in the bitmapso that its group is concerned by the allocation defined in the currentPer BSS Info field 920.

The RU Usage fields 927 defined above can be used, with AID=0 in field521 to allow any node of the BSSs indicated in BSS identifier field 921to contend for access to the RUs indicated in field 522.

In the particular case where the RU or timeslot or TXOP is let opened toaccess to all the BSSs managed by the physical AP, RU Usage field 927can be empty because all the BSSs use the same parameters.

FIG. 10 illustrates, using a flowchart, general steps of a methodaccording to the invention at one node 600 different from the AP.

At step 1000, node 600 receives a Trigger frame from an Access Point.

If the receiving node belongs to a BSS (or virtual BSS) of thetransmitting AP, the Trigger Frame is not filtered by the PHY layer asdefined in the standard. The filtering is made on so-called “colors”defined in the 802.11ax standard, which mandates that the BSS colors ofall the multiple BSSs managed by a single AP are the same.

At step 1001, node 600 analyzes the received trigger frame at the MAClayer (fields in FIG. 5a or 9 a). In particular, TA and RA fields 503,504 are analyzed.

It checks whether the received TF defines a multiple BSS scheme, fromwhich it is registered with.

It consists in checking whether one of TA or RA defines a plurality ofBSSis, e.g. a set of BSSIDs, or not, i.e. if it includes BASE_BSSID orany other multi-BSS address (e.g. a bitmap) or a multi-BSS indication912 that is enabled.

If no multiple BSS scheme is used or the multi-BSS address does notencompass the specific BSSID of node 600 (e.g. does not match BASE_BSSIDto which node 600 is registered), conventional process is implemented atstep 1010.

Otherwise, step 1002 is performed to determine whether its BSS isconcerned by the TXOP or not. This may be based on two items ofinformation:

first, whether or not the BSSID of its own BSS belongs to a set ofBSSIDs defined by the multiple BSS scheme of the trigger frame; and

second, if the Cascade Indication field 511 is set to 1 (a plurality oftimeslots is provided), whether or not the BSSID of its own BSS isindicated in at least one BSS Identifier field 921 (in which case atimeslot is allocated to its own BSS).

In case of negative determination (output “no” at test 1003), algorithmends and the node delays for the time duration specified in DurationField 502.

Otherwise, step 1004 is executed to determine the RU or RUs the node canaccess, either through contention or because the RU is scheduled to it.

In the first embodiments, the Cascade Indication field 511 is set to 1and node 600 waits for a trigger frame having a RA specifying thespecific BSSID of the BSS to which node 600 belongs. It may be the firstTF or any successive TF within the reserved and granted TXOP. Upondetecting a TF dedicated to its own BSS, the Per User Info fields 520make it possible for node 600 to know exactly the RU or RUs it canaccess (if AID=0 in field 521, the RU identified in field 522 can beaccessed through contention, while if field 521 stores the AID of node600, the RU identified in field 522 can be accessed directly withoutcontention).

In the second to fifth embodiments, the Per BSS Info field 920 of thereceived trigger frame is deeply analyzed by node 600 to determine theRU or RUs it can access.

It first requires finding the one or more Per BSS Info fields 920 thatits own BSS is concerned with. This is achieved by analyzing BSSIdentifier field 921 which should either set the specific BSSID of theBSS of node 600 or a multi-BSS address (including a broadcast address)that encompasses the specific BSSID of its own BSS.

Once such Per BSS Info fields 920 have been found, the correspondingtimeslots are determined using TF index Allocation field 922. Node 600thus now knows the timeslots its own BSS is concerned with.

Next, for each of these timeslots, node 600 determines to which RU orRUs it is eligible for access. This includes the random RUs and thescheduled RUs. This determining is made by analyzing the RU Usage fields927 defined in the found Per BSS Info fields 920. The RU or RUsidentified in field 522 for which User Identifier 521 is the AID of node600 are scheduled RU or RUs allocated to this node only. On the otherhand, the RU or RUs identified in field 522 for which User Identifier521 is AID=0 are random RU or RUs to which node 600 can access throughcontention.

As a consequence, node 600 knows the RU or RUs it can access.

In embodiments, RU allocation by the AP may provide only one RU to agiven node. In that case, once an RU node 600 can access has beenidentified, the analysis of the RU Usage fields 927 ends.

Next to step 1004, step 1005 is performed during which node 600 accessesone (or more) of the RUs determined at step 1004 and transmits itstrigger-based PPDU in uplink direction to the AP. As mentioned above,the UL PPDU shall end at the time indicated in the “HE-SIG-A Info” field512 of the Trigger frame that solicited the TXOP.

In the first, second, fourth and fifth embodiments, it may require forthe node to wait for the appropriate timeslot, as specified in field922. Preferably, node 600 uses its own specific BSSID in RA field of MACheader of UL frame (instead of BASE_BSSID as mentioned in the triggerframe). This indication helps the AP to classify the received UL framesper BSS (note also that a node is definitively identified by its AIDalong with the BSSID context).

Although the present invention has been described hereinabove withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingillustrative embodiments, which are given by way of example only andwhich are not intended to limit the scope of the invention, that beingdetermined solely by the appended claims. In particular the differentfeatures from different embodiments may be interchanged, whereappropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1. A wireless communication method in a wireless network comprising aphysical access point and a plurality of nodes organized into groups,each group being managed by the physical access point, the methodcomprising the following steps, at the physical access point: sendingone trigger frame on the wireless network to reserve a transmissionopportunity on at least one communication channel of the wirelessnetwork, the transmission opportunity including one or more resourceunits that form the communication channel and that are accessed totransmit data during the reserved transmission opportunity, the triggerframe identifying at least one node of the groups which is allowed toaccess one of the resources units to transmit data; and in response tothe trigger frame, receiving, over the resource unit during the reservedtransmission opportunity, a data frame from the at least one nodeidentified in the trigger frame; wherein each group is uniquelyidentified by a specific basic service set identification, BSSID, andwherein the specific BSSID of a group to which the at least one nodebelongs is contained in a receiver address, RA, field of the data frame.2. The method of claim 1, wherein the specific basic service setidentification, BSSID, identifying each group is derived from a baseBSSID specific to the physical access point.
 3. The method of claim 2,wherein the base BSSID is specified in a transmitter or receiver addressfield in a header of the trigger frame.
 4. The method of claim 1,wherein the trigger frame defines at least one resource unit that isaccessible by any node from any one of two or more groups.
 5. The methodof claim 4, wherein the trigger frame defines that all the resourceunits of at least one time slot are accessible by any node from any oneof two or more groups, the reserved transmission opportunity beingeither made of one time slot or split into a plurality of time slots,each resource unit being accessible by a single node during a time slotto transmit data.
 6. The method of claim 5, wherein the trigger framedefines that all the resource units in the reserved transmissionopportunity are accessible by any node from any one of two or moregroups.
 7. A wireless communication method in a wireless networkcomprising a physical access point and a plurality of nodes organizedinto groups, each group being managed by the physical access point, themethod comprising the following steps, at one node belonging to one ofthe groups: receiving a trigger frame from the physical access pointover the wireless network, the trigger frame reserving a transmissionopportunity on at least one communication channel of the wirelessnetwork, the transmission opportunity including resource units that formthe communication channel and that is accessed to transmit data duringthe reserved transmission opportunity, the trigger frame identifying atleast one node of the groups which is allowed to access the resourcesunits to transmit data; and accessing at least one of the resource unitsduring the transmission opportunity and transmitting a data frame overthe accessed resource unit to the physical access point; wherein eachgroup is uniquely identified by a specific basic service setidentification, BSSID, and wherein the specific BSSID of a group towhich the one node belongs is contained in a receiver address, RA, fieldof the data frame.
 8. The method of claim 7, wherein the specific basicservice set identification, BSSID, identifying each group is derivedfrom a base BSSID specific to the physical access point.
 9. The methodof claim 7, further comprising, at the node, determining, from thetrigger frame, that at least one resource unit is accessible by any nodefrom any one of two or more groups; and accessing this resource unit totransmit data to the physical access point.
 10. The method of claim 9,further comprising, at the node, determining, from the trigger frame,that all the resource units of at least one time slot are accessible byany node from any one of two or more groups, the reserved transmissionopportunity being either made of one time slot or split into a pluralityof time slots, each resource unit being accessible by a single nodeduring a time slot to transmit data.
 11. The method of claim 10, furthercomprising, at the node, determining, from the trigger frame, that allthe resource units in the reserved transmission opportunity areaccessible by any node from any one of two or more groups.
 12. Anon-transitory computer-readable medium storing a program which, whenexecuted by a microprocessor or computer system in a physical accesspoint of a wireless network comprising the physical access point and aplurality of nodes organized into groups, each group being managed bythe physical access point, causes the physical access point to performthe following steps: sending one trigger frame on the wireless networkto reserve a transmission opportunity on at least one communicationchannel of the wireless network, the transmission opportunity includingone or more resource units that form the communication channel and thatare accessed to transmit data during the reserved transmissionopportunity, the trigger frame identifying at least one node of thegroups which is allowed to access one of the resources units to transmitdata; and in response to the trigger frame, receiving, over the resourceunit during the reserved transmission opportunity, a data frame from theat least one node identified in the trigger frame; wherein each group isuniquely identified by a specific basic service set identification,BSSID, and wherein the specific BSSID of a group to which the at leastone node belongs is contained in a receiver address, RA, field of thedata frame.
 13. A communication device acting as a physical access pointin a wireless network also comprising a plurality of nodes organizedinto groups, each group being managed by the physical access point, thecommunication device acting as a physical access point comprising atleast one microprocessor configured for carrying out the steps of:sending one trigger frame on the wireless network to reserve atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including one or moreresource units that form the communication channel and that are accessedto transmit data during the reserved transmission opportunity, thetrigger frame identifying at least one node of the groups which isallowed to access one of the resources units to transmit data; and inresponse to the trigger frame, receiving, over the resource units duringthe reserved transmission opportunity, a data frame from the at leastone node identified in the trigger frame; wherein each group is uniquelyidentified by a specific basic service set identification, BSSID, andwherein the specific BSSID of a group to which the at least one nodebelongs is contained in a receiver address, RA, field of the data frame.14. A communication device in a wireless network comprising a physicalaccess point and a plurality of nodes organized into groups, each groupbeing managed by the physical access point, the communication devicebeing one node belonging to one of the groups and comprising at leastone microprocessor configured for carrying out the steps of: receiving atrigger frame from the physical access point over the wireless network,the trigger frame reserving a transmission opportunity on at least onecommunication channel of the wireless network, the transmissionopportunity including resource units that form the communication channeland that is accessed to transmit data during the reserved transmissionopportunity, the trigger frame identifying at least one node of thegroups which is allowed to access the resources units to transmit data;and accessing at least one of the resource units during the transmissionopportunity and transmitting a data frame over the accessed resourceunit to the physical access point; wherein each group is uniquelyidentified by a specific basic service set identification, BSSID, andwherein the specific BSSID of a group to which the one node belongs iscontained in a receiver address, RA, field of the data frame.
 15. Themethod of claim 1, wherein each group is managed by a virtual accesspoint implemented in the physical access point.
 16. A non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a node of a wireless networkcomprising a physical access point and a plurality of nodes organizedinto groups, each group being managed by the physical access point,causes the node, which belongs to one of the groups, to perform thefollowing steps: receiving a trigger frame from the physical accesspoint over the wireless network, the trigger frame reserving atransmission opportunity on at least one communication channel of thewireless network, the transmission opportunity including resource unitsthat form the communication channel and that is accessed to transmitdata during the reserved transmission opportunity, the trigger frameidentifying at least one node of the groups which is allowed to accessthe resources units to transmit data; and accessing at least one of theresource units during the transmission opportunity and transmitting adata frame over the accessed resource unit to the physical access point;wherein each group is uniquely identified by a specific basic serviceset identification, BSSID, and wherein the specific BSSID of a group towhich the one node belongs is contained in a receiver address, RA, fieldof the data frame.
 17. The method of claim 7, wherein each group ismanaged by a virtual access point implemented in the physical accesspoint.